This project will continue the synthesis of affinity labeling progesterone and estrogen derivatives in a three-pronged effort to study: (a) the mechanism of steroid binding to macromolecular steroid binding sites, (b) the mechanism of steroid hormone action via receptor proteins, (c) and to provide new steroid analogs intended for study of hormonal regulation of the mammalian reproductive system. We shall continue to purify receptor and enzyme proteins with our new disulfide affinity chromatography technique in order to examine the topographical elements of the steroid binding sites by affinity labeling, to determine the precise molecular factors responsible for specificity of the binding sites. This approach will enable us to rationally design and synthesize new steroids for specific biological effects. We shall attempt to define the exact mechanism by which previously synthesized affinity labeling steroids terminate pregnancy in rats, following intrauterine administration. The reaction of new progesterone affinity labeling analogs with the pituitary-hypothalmic system will be newly studied in vivo and in vitro to determine whether these centers can be altered with the chemically reactive progestin and estrogen analogs. For example, our recently synthesized medroxyprogesterone 17-bromoacetate (a Provera affinity labeling analog) will be used in this manner. This project is designed to gain further insight into the relationship between the nature of steroid-protein interactions at the molecular level, and steroid hormone action at the biological level.